PHILADELPHIA (CBS) — As Hurricane Sandy approaches, the city of Philadelphia is closing government offices, court houses, mass transit and public and Archdiocesan schools on Monday. And Mayor Michael Nutter continues to urge residents to be ready.

After SEPTA (read SEPTA Shutdowns) and the School District announced their closures (read Schools Closed), Mayor Nutter quickly followed suit, closing the city government down for all but the most essential services — police, fire, prisons and PGW.

“All other public employees should check with their supervisors,” Nutter said, “but should expect not to be at work.”

Three city shelters – at Roxborough, West Philadelphia and Fels high schools — are now open.

Water Department crews continue to clear inlets, and trash pickup Monday and Tuesday has been canceled.

Mayor Nutter urged everyone to stay home.

“Stay off the roads,” the mayor said, “so that our first responders are not putting their lives at risk should someone find themselves inadvertently in a dangerous circumstance or condition.”

The city’s 311 non-emergency service has expanded hours and officials are urging residents to use that rather than 911, unless it’s a true emergency.